Communications systems for distributing television, telephony, and data signals often comprise coaxial cables over which television and/or communications signals (hereinafter collectively data signals) are carried. Coaxial cables conventionally carry, in addition to data signals, a low frequency AC power signal from for powering line extending amplifiers that amplify the data signals to avoid signal degradation as the data signals propagate through the network and/or for powering the network interface unit located at the customer premises. A communications system comprised of coaxial cables will be referred to as a coaxial network.
Many modern communications systems comprise both coaxial cables and fiber optic cables. The fiber optic cables distribute the data signal from the cable headend to various points throughout the network, at which point the data signals are converted to a format appropriate for transmission over existing coaxial cables. The equipment involved in converting the data signals from fiber optic format to coaxial format will be referred to herein as fiber optic cable support equipment. Both the coaxial cables and the fiber optic cable support equipment require an appropriate AC power signal for operation. A communications system comprised of both fiber optic and coaxial cables will be referred to herein as a hybrid fiber-coax (HFC) network.
The AC power signals used by coaxial and HFC networks are conventionally provided by power supplies distributed throughout the communications system. These conventional power supplies generate their power from a utility power source, but contain batteries to provide standby service in the event of a utility power disruption. Such power supplies will be referred to herein as uninterruptible power supplies, or UPS's.
The reliability of a coaxial or HFC network depends in large part on the reliability of the AC power signal used by the various components of the network; as such networks are modified for the transmission of communications signals in addition to television signals, the tolerance for network failures decreases. The reliability of the UPS's used in such networks is thus an important consideration.
The efficiency with which the UPS's generate the AC power signals is also significant because the utility power signals are all passed through the UPS's to obtain the AC power signals used by the network. UPS's must also meet a satisfy a number of performance criteria to ensure proper operation of the network components and thus reliable distribution of the data signals carried by the network.
In addition, a large number of UPS's are distributed throughout a typical coaxial or HFC network. The cost of purchasing and maintaining these UPS's is thus a significant portion of the costs of operating the network.
The need thus exists for UPS's for coaxial and HFC networks having improved reliability and efficiency and acceptable performance but which maintain network operating costs at a desirable level.